Transaminases (E.C. 2.6.1) catalyze the transfer of an amino group, a pair of electrons, and a proton from a primary amine of an amino donor substrate to the carbonyl group of an amino acceptor molecule as shown in Scheme 1.

An amino acceptor compound (I) (which is the precursor of the desired chiral amine product (III)) is reacted with an amino donor compound (II). The transaminase catalyzes the transfer of the amine group of the amino donor (II) to the keto group of the amino acceptor (I). The reaction results in the desired chiral amine product compound (III) and a new amino acceptor compound (IV) with a ketone group as a by-product.
Wild-type transaminases having the ability to catalyze a reaction of Scheme 1 have been isolated from various microorganisms, including, but not limited to, Alcaligenes denitrificans, Bordetella bronchiseptica, Bordetella parapertussis, Brucella melitensis, Burkholderia malle, Burkholderia pseudomallei, Chromobacterium violaceum, Oceanicola granulosus HTCC2516, Oceanobacter sp. RED65, Oceanospirillum sp. MED92, Pseudomonas putida, Ralstonia solanacearum, Rhizobium meliloti, Rhizobium sp. (strain NGR234), Bacillus thuringensis, Klebsiella pneumonia, and Vibrio fluvialis (see e.g., Shin et al., 2001, Biosci. Biotechnol, Biochem. 65:1782-1788). Several of these wild-type transaminase genes and encoded polypeptides have been sequenced, including e.g., Ralstonia solanacearum (Genbank Acc. No. YP_002257813.1, GI:207739420), Burkholderia pseudomallei 1710b (Genbank Acc. No. ABA47738.1, GI:76578263), Bordetella petrii (Genbank Acc. No. AM902716.1, GI:163258032), and Vibrio fluvialis (Genbank Acc. No. AEA39183.1, GI: 327207066). Two wild-type transaminases of classes EC 2.6.1.18 and EC 2.6.1-19, have been crystallized and structurally characterized (see e.g., Yonaha et al., 1983, Agric. Biol. Chem. 47 (10):2257-2265).
The wild-type transaminase from Vibrio fluvialis J517 is an ω-amino acid:pyruvate transaminase (E.C. 2.6.1.18) that uses pyridoxal-5′-phosphate as cofactor to catalyze the reaction of Scheme 2.

This wild-type transaminase from Vibrio fluvialis also has been reported to show catalytic activity toward aliphatic amino donors that do not have a carboxyl group.
Chiral amine compounds are frequently used in the pharmaceutical, agrochemical and chemical industries as intermediates or synthons for the preparation of various pharmaceuticals, such as cephalosporine or pyrrolidine derivatives. A great number of these industrial applications of chiral amine compounds involve using only one particular optically active form, e.g., only the (R) or the (S) enantiomer is physiologically active. Transaminases have potential industrial use for the stereoselective synthesis of optically pure chiral amine compounds, such as in the enantiomeric enrichment of amino acids (see e.g., Shin et al., 2001, Biosci. Biotechnol. Biochem. 65:1782-1788; Iwasaki et al., 2003, Biotech. Lett. 25:1843-1846; Iwasaki et al., 2004, Appl. Microb. Biotech. 69:499-505, Yun et al., 2004, Appl. Environ. Microbiol. 70:2529-2534; and Hwang et al., 2004, Enzyme Microbiol. Technol. 34:429-426).
Other examples of the use of transaminases include the preparation of intermediates and precursors of pregabalin (e.g., WO 2008/127646); the enzymatic transamination of cyclopamine analogs (e.g., WO 2011/017551); the stereospecific synthesis and enantiomeric enrichment of β-amino acids (e.g., WO 2005/005633); the enantiomeric enrichment of amines (e.g., U.S. Pat. Nos. 4,950,606; 5,300,437; and 5,169,780); and the production of amino acids and derivatives (e.g., U.S. Pat. Nos. 5,316,943; 4,518,692; 4,826,766; 6,197,558; and 4,600,692).
However, transaminases used to catalyze reactions for the preparation of chiral amine compounds can have properties that are undesirable for commercial applications, such as instability to industrially useful process conditions (e.g., solvent, temperature) and narrow substrate recognition. Thus, there is a need for other types of transaminase biocatalysts that can be used in industrial processes for preparing chiral amines compounds in an optically active form.